Flexible line guide for industrial robot

ABSTRACT

Guide ( 20 ) for a loop of a flexible line ( 40 ) between a pair of rotatable parts ( 12, 14 ) of an industrial robot ( 10 ) that rotate relative to one another around an axis ( 18 ), whereby the loop includes a pair of strands ( 42, 44 ) of the line joined by a bend ( 46 ) that extend around axis ( 18 ) with their outsides engaged with the respective parts so that the loop is caused to perform a movement around the axis ( 18 ) when the parts rotate relative to one another. To reduce wear on the cover of the line and to facilitate replacing the line, it is suggested that, among other things, the engagement consists of a separate groove ( 22, 32 ) arranged for each strand ( 42  respectively  44 ).

TECHNICAL FIELD

The invention relates to a flexible line guide for an industrial robotaccording to the introduction to claim 1.

Such guides are commonly used for carrying an outer line in the form ofa welding cable or a pressurised fluid line, for example, between thefoot and the rotating upper section of an industrial robot.

PRIOR ART

Guides of this type are known, for example, from U.S. Pat. No. 5,694,813and EP-A-0 552 688. A disadvantage of such known guides is that theouter peripheral side of the loop, especially at the bend, must beguided by the inside of a stationary cylindrical wall or a cylindricalwall that rotates together upper section of the robot, in order not todeviate outwards from the path of movement around the axis, which causesundesirable friction and wear on the covering of the line.

SUMMARY OF THE INVENTION

One objective of the present invention is to achieve a guide of the typestated in the introduction that significantly reduces wear and thusincreases the working life of the covering of the line.

A second objective is to obtain a guide that makes it easy to replacethe line.

These are achieved by means of the features that are stated in thefollowing claims.

According to an aspect of the invention, a separate groove for everystrand is the only engagement provided between the cable loop and theparts that rotate relative to one another. In this way, none of thestrands nor the bend come into sliding contact with a wall, as is thecase in the prior art, so that essentially all the relative movementbetween the covering of the line and the parts that rotate relative toone another that causes wear is eliminated. A further advantage withthis arrangement is that thanks to the resulting free space between thegrooves, the line is easier to remove from the guide and be put backthere when it needs to be replaced.

According to one preferred embodiment of the invention, the grooves havedifferent mutual radii so that the bend will be angled relative to thecommon axis of rotation. In this way, the radius of curvature of thebend can also be increased advantageously at a pre-determined axialdistance between the grooves. This ensures partly that the insignificantrelative movement that does nevertheless occur between the line and thegroove takes place primarily only at the transition between the strandand the bend of the groove with the smaller radius and partly that thebend has less of a tendency to deviate at a tangent outwards from thepath of rotation since it leans inwards from the largest radius.

If the grooves are formed in groove elements that can be mounted on theoutsides of the respective parts in a removable fashion, an existingrobot can later easily have an additional guide fitted according to theinvention.

Other features and advantages of the invention are evident from theclaims and the following detailed description.

DESCRIPTION OF THE DRAWINGS

Embodiments of the invention is described by way of example in detailbelow with reference to the enclosed drawings, where

FIG. 1 is a diagrammatic view from behind of an industrial robot withsome parts removed fitted with a guide according to the invention and;

FIG. 2 is a simplified diagrammatic view of the guide according to FIG.1 seen from above at an oblique angle;

FIG. 3 is a view partly in cross-section and with parts removed of onepreferred embodiment of a groove element according to the invention;

FIG. 4 is a cross-sectional view of an alternative embodiment of agroove element according to the invention;

FIG. 5 is a view seen from the front and from above at an oblique angleof a foot and the frame element of an industrial robot equipped with agroove element according FIG. 3; and

FIG. 6 is a side view of a guide according to the invention providedwith a support for an upper part of the guided line.

DETAILED DESCRIPTION OF EMBODIMENTS

In the diagrammatic representation according to FIG. 1, an industrialrobot is generally designated 10 and includes a lower section 12 in theform of a stationary foot and a rotating upper section 14 in the form ofa frame unit that rotates relative to the foot around a vertical axis18. The lower section 12 and the upper section 14 are joined with oneanother via a bearing arrangement 16 that is not shown in any greaterdetail.

A flexible, continuous line 40 with a covering that is not shown indetail extends between the lower section 12 and the upper section 14.This covering can typically enclose a welding cable, but also othertypes of lines for, for example, transport of fluids or other media. Thecovering can also be a separate outer covering for that part of the linethat extends between parts 12 and 14 (not shown). In order for the upperpart 14 to rotate without hinder for approximately 180° clock-wise and180° counter-clockwise from the mid-point of rotation in FIG. 1, a slackof the line 40 to accommodate the movement of rotation extends in a loopround about 90° of the space between parts 12 and 14. More specifically,the loop has a lower partly circular strand 42, an upper partly circularstrand 44 and a bend or nose 46 of line 40 that joins the strands. Whenthe upper part 14 rotates counter-clockwise, the upper strand 44 istransferred to the lower strand 42 via the bend 46 “rolling forwards”.When part 14 rotates clockwise, the lower strand 42 is transferred tothe upper strand 44 in the reversed manner via the bend 46 “rollingbackwards”

According to the invention, strands 42, 44 are guided by theirengagement with their own groove 22 and 32 respectively. In the examplesof the embodiments shown, grooves 22, 32 both extend in a circular archaround a front of the robot 10 when this is positioned in the middle ofits field of rotation.

According to the invention, grooves 22 and 32 have different radii R1and R2 respectively with regard to their common axis 18. The lowergroove has the larger radius in the example shown, but the opposite caseis also possible. It is also possible to have grooves with differentradii in the same radial plane with regard to axis 18, so that the partsof the loops and the bend run in a common horizontal plane around therobot (not shown).

The diagrammatic representations in FIGS. 1 and 2 show grooves 22; 32 inprincipal only in the form of thin-walled channels with a flat bottomwall 24, 34 and outwardly angled side walls, flanks or flanges 26, 28;36, 38. In these cases, the groove can be made of, for example, foldedand possibly welded steel plate that can be attached to the associatedparts 12, 14 respectively by means of screw fittings. However, it isalso possible to make the grooves or channels of plastic material.

The cross-section of the groove can be varied to achieve an optimalcompromise between minimal wear and best guidance, especially betweenthe transition of the line between the strand and the bend in the groovewith the smallest radius R2. According to one preferred embodiment ofthe invention shown in FIGS. 3 and 5, such an optimised groove is formedin groove element 21 from extruded and bent light metal, preferablyaluminium.

In the embodiment shown in FIG. 3, each groove is delimited by anessentially vertical inner flange 28 and an outer flange 26 that isangled outwards from the bottom wall 24. The inner sides of flanges 26,28 are slightly convex to securely fix the cross-section of line 40 andguide line 40 down towards the bottom of the groove. However, as hasalready been mentioned, this also facilitates fitting or removing line40 due to the free space between the grooves. In addition, the free endsof the outer flange 26 have a wider section that provides extrarigidity, that forms a gently rounded finish to reduce the risk ofpersonal injuries, and that forms an end stop that can help prevent line40 from jumping out from the groove if for some reason—such as due to aforeign object in the groove—it momentarily comes under pressure to bepushed out from the groove.

Each groove element 21 (FIG. 3) is attached to the associated part 12 ofrobot 10 from the outside of the robot by means of, for example, a screwfitting and is suitably positioned at the peripheral edge of associatedpart 12 via a peripheral corner recess 27 formed on the outside of thebottom 24 of the groove.

The angle of opening and the width between the flanks of the groove canalso be formed so that the cross-section of the line snaps firmly intothe groove. The downwards facing groove especially can be formed in thisway to prevent the line falling out from the groove due to its weight.

Since an operator or service technician will for various reasons fromtime to time need to climb up onto the robot and can then need to usethe groove elements as foot supports, these are suitably dimensioned tohave the size and durability to match this need.

So that the upwards facing groove of the guide will not collect liquidsand foreign objects, such as welding sparks and similar, this groovepreferably has openings running through it. The openings can, in a waynot shown, be accommodated in the bottom and in the flanges of thealready described embodiments made of steel plate and light metal.

In the embodiment shown in FIG. 4, the groove element is made of awelded steel wire construction. In this case, the groove is formed fromessentially a half-circular arch-shape of steel wires 50, 52 that arecarried on steel wires 54 (only one is shown) that are at right anglesto these and that are evenly spaced peripherally, and that are shaped tothe desired profile of the groove. As a consequence, the desiredopenings in the groove are formed by the gaps 56 between the steelwires.

The groove elements can, however, be formed in other ways. For example,they can be formed by straight sections that are welded together (notshown). The groove need not be continuous either, but can extend aroundthe groove periphery in the form of discrete elements with the gapbetween them (not shown) forming the openings.

FIG. 6 shows another embodiment of a guide according to the invention inthe position at the end of its rotation (180° clockwise rotation) wherethe major portion of line 40 is in the upper strand 44. To avoid therisk that this might fall down from the upper groove 32, a lower support60 is arranged for line 40. In the preferred embodiment, lower support60 has the form of a hanging support comprised of a bent tube 62. Tube62 extends concentrically to the upper groove 32 in such a way that itcaptures and holds the upper strand 44 from below when this tends toexit the groove due to its weight. Tube 62 suitably has a smaller radiusthan the radius of upper groove 32. If lower groove 22 additionally hasa larger radius that upper groove 32, as is preferable, the bend of line40 is angled inwards towards the upper groove without the risk of comingin contact with tube 62.

What is claimed is:
 1. Guide for a loop of a flexible continuous linebetween a pair of rotatable parts of an industrial robot that rotaterelative to one another around an axis, whereby the loop includes a pairof strands of the line joined by a bend that extend around the axis,said guide comprising: means engaging outer sides of each of the strandswith a respective part so that the loop is caused to perform a movementaround the axis when the parts rotate relative to one another, whereinsaid engaging means comprises a pair of spaced and separate rigidannular grooves facing each other, a first of said pair of groovesengaging a first of the pair of strands, and a second of said pair ofgrooves engaging a second of the pair of strands, and wherein thegrooves extend with mutually different distances from the axis.
 2. Theguide according to claim 1, wherein the grooves comprise an upper grooveand a lower groove where the lower groove extends at a greater distancefrom the axis that the upper groove.
 3. The guide according to claim 2,wherein there is an underlying support for the upper strand of the linewhere the underlying support extends concentrically along and below theupper groove.
 4. The guide according to claim 1, wherein the groovescomprise an upper groove and a lower groove where the upper grooveextends at a greater distance from the axis that the lower groove. 5.The guide according to claim 1, wherein the grooves extend in a commonradial plane relative to the axis.
 6. The guide according to claim 1,wherein at least one of the grooves includes a groove element that canbe attached to and removes from the outer surface of the respectivepart.
 7. The guide according to claim 6, wherein the groove elementincludes an extruded and bent light metal element.
 8. The guideaccording to claim 6, wherein a bottom side of the, groove element has aperipheral recess arranged to position the groove element at aperipheral edge of the respective part.
 9. The guide according to claim1, wherein at least one of the grooves extends with substantially flatoutwardly facing flanges from a substantially flat bottom of the groove.10. The guide according to claim 1, wherein at least one upwardly facinggroove of said grooves has openings running through said upwardly facinggroove.
 11. The guide according to claim 1, wherein at least one of thegrooves is formed from a welded wire construction.
 12. Guide for a loopof a flexible continuous line between a pair of rotatable parts of anindustrial robot that rotate relative to one another around an axis,whereby the loop includes a pair of strands of the line joined by a bendthat extend around the axis, said guide comprising: means engaging outersides of each of the strands with a respective part so that the loop iscaused to perform a movement around the axis when the parts rotaterelative to one another, wherein said engaging means comprises a pair ofspaced and separate rigid annular grooves facing each other, a first ofsaid pair of grooves engaging a first of the pair of strands, and asecond of said pair of grooves engaging a second of the pair of strandsand wherein at least one of the grooves extends about 180° around therobot.
 13. Guide for a loop of a flexible continuous line between a pairof rotatable parts of an industrial robot that rotate relative to oneanother around an axis, whereby the loop includes a pair of strands ofthe line joined by a bend that extend around the axis, said guidecomprising: means engaging outer sides of each of the strands with arespective part so that the loop is caused to perform a movement aroundthe axis when the parts rotate relative to one another, wherein saidengaging means comprises a pair of spaced and separate rigid annulargrooves facing each other, a first of said pair of grooves engaging afirst of the pair of strands, and a second of said pair of groovesengaging a second of the pair of strands, and wherein at least one ofthe grooves has convex flanks.